Photochemical reactions use light as a source of energy to promote chemical processes. Ultraviolet (UV) and visible light are widely used in chemical synthesis both in laboratories and in commercial manufacturing. Well known photochemical reactions include photodimerization, photopolymerization, photohalogenation, photoisomerization and photodegradation. For example, cyclobutanetetracarboxylic dianhydride can be synthesized by photodimerization of maleic anhydride in a glass reactor using a mercury UV lamp (P. Boule et al., Tetrahedron Letters, Volume 11, pages 865 to 868, (1976)). Most of the vitamin D production in the United States is based on UV photolysis in a quartz vessel using light between 275 and 300 nm.
In photochlorination, chlorine (Cl2) reacts with a saturated or unsaturated starting material, in the presence of a ultraviolet light source. This process is widely used to form carbon-chlorine bonds under mild conditions (e.g., room temperature) compared to the elevated temperatures normally required for thermal chlorination (R. Roberts et al., Applications of Photochemistry, TECHNOMIC Publishing Co., Inc. 1984). For example, E. Tschuikow-Roux, et al. (J. Phys. Chem., Volume 88, pages 1408 to 1414 (1984)) report photochlorination of chloroethane and Walling et al. (J. Amer. Chem. Soc., Volume 79, pages 4181 to 4187 (1957)) report photochlorination of certain substituted toluenes. U.S. Pat. No. 5,190,626 describes the use of photochlorination in removing unsaturated compounds such as vinylidine chloride from CCl2FCH3 product. Chlorine-containing compounds such as CCl2FCH3 may be readily converted to olefinic compounds (e.g., CClF═CH2) by dehydrohalogenation or to fluorine-containing compounds (e.g., CF3CH3) by fluorination using hydrogen fluoride (HF).
Typically in photochlorinations, light from a suitable source (e.g., an incandescent bulb or a UV lamp) is directed through a reactor wall to interact with the reactants therein. The portion of the reactor wall through which the light passes must have a suitable transmittance to allow light of a wavelength required for the photochlorination to enter the reactor. Typically, quartz or borosilicate glass like Pyrex™ glass have been employed as transparent materials. Quartz is expensive, but has a low cut-off wavelength at about 160 nm; Pyrex™ glass is less expensive, but has a relatively high cut-off wavelength at about 275 nm. Due to their reactivity, quartz and Pyrex are not appropriate materials of construction for chemical reactions involving base or HF. There is a need for additional materials which can be used for this purpose in photochemical reactions (e.g., photochlorinations).